ABSTRACT
Inseticidas podem causar mortalidade e efeitos deletérios em percevejos predadores. Por isso investigou-se o efeito de cinco concentrações de permetrina aplicadas em ninfas de terceiro estádio de Supputius cincticeps (Stål) (Heteroptera: Pentatomidae) em sua ativação ovariana. Essas ninfas receberam aplicação tópica de permetrina nas seguintes concentrações (mg i.a./ml): 10ù7, 10ù6, 10ù5, 10ù4, 10ù3. O comprimento dos ovários e o número de ovócitos foram quantificados após a primeira postura. O comprimento do ovário variou de 5,7 mm na concentração de 10ù4 mg i.a./ml a 6,4 mm na concentração de 10ù7 mg i.a./ml, com valores semelhantes para as outras concentrações de permetrina e controle. O número de ovócitos por fêmea variou de 13,5 (10ù3 mg i.a./ml) a 29,2 no controle, com diferenças significativas entre concentrações. O número de ovócitos por fêmea, proveniente de ninfas expostas a concentração de 10ù5 mg i.a./ml, foi semelhante àquele do controle. No entanto, o menor número de ovócitos por fêmea, provenientes de ninfas expostas a outras concentrações de permetrina, sugere que esse inseticida pode afetar a capacidade reprodutiva. Esses resultados são discutidos em relação à tolerância de Heteroptera predador aos inseticidas e a possível ocorrência de hormese.
Subject(s)
Animals , Female , Heteroptera/drug effects , Insecticides/pharmacology , Ovary/drug effects , Permethrin/pharmacology , Insecticides/administration & dosage , Nymph/drug effects , Oocytes , Ovary/growth & development , Permethrin/administration & dosage , Reproduction/drug effectsABSTRACT
The stinkbug Supputius cincticeps (Stål) (Heteroptera: Pentatomidae) can be found in agricultural and forest ecosystems feeding primarily on larvae of Coleoptera and Lepidoptera, where it can be exposed to insecticide applications. This study therefore aimed to evaluate the reproductive potential of'S. cincticeps after exposition to sublethal doses of permethrin (5.74 x 10-3, 5.74 x 10-2, 5.74 x 10-1, 5.74 and 57.44 ppb) through the use of a fertility life table. The development cycle of this predator was determined in order to calculate its net reproductive rate (R0), the infinitesimal (rm) and finite (λ) rates of increase in addition to mean generation time (T). The net reproductive (18.31), infinitesimal (rm) (0.050) and finite (λ) (1.051) rates of increase were higher, while generation time (57.93 days) was shorter for S. cincticeps exposed to 5.74x10-1 ppb of permethrin than in the control. This indicates a higher rate of population increase of this predator when exposed to this permethrin dose.
Subject(s)
Animals , Female , Heteroptera/drug effects , Insecticides/pharmacology , Permethrin/pharmacology , Dose-Response Relationship, Drug , Fertility/drug effects , Life Expectancy , Larva/drug effects , Time FactorsABSTRACT
BACKGROUND & OBJECTIVES: Anopheles stephensi and A. culicifacies are the two major vectors of malaria in Karnataka. These mosquito populations are continuously being exposed directly or indirectly to different insecticides including the most effective pyrethroids. Therefore, there is a threat of insecticide resistance development. We subjected these vectors to larval bioassay using two popular pyrethroids viz deltamethrin and permethrin. An attempt was also made to correlate the activities of certain detoxifying enzymes such as A- esterase, B-esterase, glutathione-S transferase (GST) and glucose-6-phosphate dehydrogenase (G6PD) with the tolerance levels of the two vectors. METHODS: Larval bioassay was carried out following the standard WHO procedure on field-collected larvae. The LC50 and LC90 values were calculated following Probit analysis. Biochemical estimations were done with a U V spectrophotometer and the isozyme studies employing native polyacrylamide gel electrophoresis (PAGE). RESULTS: The results of the larval bioassay revealed that A. stephensi has more tolerance to deltamethrin than A. culicifacies and vice versa for permethrin. Biochemical estimations revealed significantly (P < 0.05) higher levels of A-esterase and GST activity in A. stephensi whereas A. culicifacies showed significantly higher (P < 0.05) levels of B-esterase and G6PD activity. The total larval protein assayed was found to be more (P < 0.05) in A. stephensi. The isozyme profiles also revealed difference in mobility, intensity and the number of bands. INTERPRETATION & CONCLUSION: As these malaria vectors are exposed to different kinds of insecticides, they develop increased enzyme activities to overcome the insecticide pressure. This has enhanced the tolerance level against the pyrethroids tested. Thus, A. stephensi was found to be tolerant to deltamethrin depicting a higher activity of A-esterase and GST enzymes, whereas the higher activity of B-esterase and G6PD has resulted in the development of tolerance to permethrin in A. culicifacies.